Transmission assembly

ABSTRACT

An improved transmission assembly includes a pair of variable diameter drive pulleys having effective diameters which can be changed in response to a command signal to vary the speed of rotation of an output member relative to the speed of rotation of an input member. To accomplish this, the command signal effects operation of a reversible servomotor to operate drive assemblies. One of these drive assemblies moves a section of one drive pulley toward another section of the drive pulley to increase the effective diameter of this drive pulley. Operation of the drive assemblies also moves a section of the other drive pulley away from an associated section of the pulley to decrease the effective diameter of this drive pulley. As the sections of the drive pulleys are being moved, a signal generator provides a feedback signal which varies with variations in the effective diameters of the drive pulleys. An error detector interrupts operation of the servomotor when the feedback signal is a predetermined function of the command signal. A belt stretch compensator assembly is provided to increase the effective diameters of both drive pulleys in response to an increase in the effective length of a drivebelt extending between the drive pulleys.

United States Patent Ebersold [54] TRANSMISSION ASSEMBLY [72] Inventor:Robert C. Ebersold, Novelty, Ohio [73] Assignee: The Warner 8: SwaseyCompany, Cleveland, Ohio [22] Filed: Apr. 8, 1970 [21] Appl. No.: 26,675

Primary Examiner-Leonard H. Gerin A ttomey-Yount and Tarolli 1 Feb. 22,1972 [57] ABSTRACT An improved transmission assembly includes a pair ofvariable diameter drive pulleys having effective diameters which can bechanged in response to a command signal to vary the speed of rotation ofan output member relative to the speed of rota tion of an input member.To accomplish this, the command signal effects operation of areversilble servomotor to operate drive assemblies. One of these driveassemblies moves a section of one drive pulley toward another section ofthe drive pulley to increase the effective diameter of this drivepulley. Operation of the drive assemblies also moves a section of theother drive pulley away from an associated section of the pulley todecrease the effective diameter of this drive pulley. As the sections ofthe drive pulleys are being moved, a signal generator provides afeedback signal which varies with variations in the effective diametersof the drive pulleys. An error detector interrupts operation of theservomotor when the feedback signal is a predetermined function of thecommand signal. A belt stretch compensator assembly is provided toincrease the effective diameters of both drive pulleys in response to anincrease in the effective length of a drivebelt extending between thedrive pulleys.

21 Claims, 6 Drawing Figures mimwrzazzjm 3,643,519

' sum 1 HF d INVE/W'UR RUBERT C. EBERSOLO ATTORNEYS TRANSMISSIONASSEMBLY This invention relates to a transmission assembly which isoperable to vary the speed of an output member relative to the speed ofan input member by varying the effective diameter of at least one pulleyof a pair of pulleys.

It is an object of this invention to provide a new and improvedtransmission assembly for automatically varying the speed of an outputmember relative to the speed of an input member in response to a commandsignal by varying the effective diameter of a drive pulley which isoperatively connected to one of the members.

Another object of this invention is to provide a new and improvedtransmission assembly including first and second pulleys operativelyconnected to input and output members and a drive means operable to varythe effective diameters of the pulleys and wherein a control meansoperates the drive means to vary the effective diameters of the firstand second pulleys in response to a command signal.

Another object of this invention is to provide a new and improvedtransmission assembly in accordance with the next preceding objectwherein the control means includes a servomotor for operating the drivemeans in response to the command signal to effect relative movementbetween sections of the pulleys'ra signal generator for providing afeedback signal which varies as a function of variations in the relativepositions of the sections of the pulleys, and an error detectorresponsive to the feedback and command signals to interrupt operation ofthe servomotor when the feedback signal is a predetermined function ofthe command signal.

Another object of this invention is to provide a new and improvedtransmission assembly for varying the speed of an output member relativeto the speed of an input member including first and second drive pulleyswith a drivebelt extending therebetween and a compensator assembly forautomatically increasing the effective diameter of at least one of thedrive pulleys in response to an increase in the effective length of thedrivebelt to thereby maintain the drivebelt taut.

Another object of this invention is to provide a new and improvedtransmission assembly for varying the speed of an output member relativeto the speed of an input member including a first drive pulley having aplurality of sections which are movable relative to each other to varythe effective diameter of the first drive pulley, a second drive pulleyhaving sections which are movable relative to each other to vary theeffective diameter of the second drive pulley, a drivebelt operativelyinterconnecting the drive pulleys, and a pair of drive assemblies eachof which is associated with one of the drive pulleys and includes anexternally threaded shaft which cooperates with an internally threadednut and is operable to effect relative movement between the sections ofthe associated drive pulley and wherein a compensator assembly isoperable to apply biasing forces to the internally threaded nuts toeffect an increase in the effective diameters of the drive pulleys in vresponse to an increase in the effective length of the drivebelt.

These and other objects and features of the invention will become moreapparent upon a consideration of the following description taken inconnection with the accompanying drawings wherein:

FIG. 1 is a fragmentary elevational view of a transmission assemblyconstructed in accordance with the present inventron;

FIG. 2 is a fragmentary view, taken generally along the line 2-2 of FIG.1, illustrating the relationship between a pair of variable diameterdrive pulleys and a control mechanism for operating a pair of driveassemblies to vary the effective diameters of the drive pulleys inresponse to a command signal;

FIG. 3 is a schematicized fragmentary sectional view, taken generallyalong the line 33 of FIG. 4, illustrating a servomotor control assemblyfor operating the drive assemblies of FIG. 2 to vary the effectivediameters of the drive pulleys;

FIG. 4 is a plan view, taken generally along the line 44 of FIG. 3,illustrating a gear train for drivingly connecting the servomotor andcontrol assembly of FIG. 3 with a main control pulley;

FIG. 5 is an enlarged, partially broken away fragmentary view, takengenerally along the line 5-5 of FIG. 1, illustrating the relationshipbetween an output shaft, one of the drive pulleys, and a drive assemblyfor varying the effective diameter of this drive pulley; and

FIG. 6 is an enlarged, partially broken away fragmentary view, takengenerally along the line 6-6 of FIG. 1, illustrating the relationshipbetween an output shaft, one of the drive pulleys, and a drive assemblyfor varying the effective diameter of this drive pulley.

The present invention provides a new and improved transmission assemblyfor automatically varying the speed of an output shaft relative to thespeed of an input shaft in response to a command signal. Thetransmission assembly includes variable diameter input and output drivepulleys. Drive assemblies are associated with these drive pulleys andare operable by a control assembly to vary the effective diameters ofthe drive pulleys. The control assembly includes a servomotor which isoperated in response to a command signal to operate the drive assembliesand vary the effective diameters of the drive pulleys. When theeffective diameter of the drive pulleys corresponds to a predeterminedfunction of the command signal, an error detector interrupts operationof the servomotor.

A specific preferred embodiment of a transmission assembly constructedin accordance with the present invention is illustrated in FIGS. 1 and2. The transmission assembly 10 is operable to transmit torque from aninput shaft 12 to an output shaft 14 by means of a pair of variablediameter drive pulleys l6 and 18 (see FIG. 2). The drive pulleys 16 and18 are drivingly interconnected by a main drivebelt 20. The speed of theoutput shaft 14 is varied relative to the speed of the input shaft 12 byoperating drive assemblies Y24 and 26 which are associated with thedrive pulleys l6 and 18, respectively, to vary the effective diametersof the drive pulleys. The drive assemblies 24 and 26 are operated by acontrol assembly 30 in response to a command signal to vary the speed ofrotation of the output shaft 14 relative to the input shaft 12 by anamount which is a predetermined function of the command signal.

To enable the effective diameters of the drive pulleys 16 and 18 to bevaried, the drive pulleys include sections 34 and 36 which are movableaxially relative to fixed sections 38 and 40 upon operation of the driveassemblies 24 and 26. The effective diameter of the drive pulley 16 isincreased by operating the drive assembly 24 to move the section 34 ofthe drive pulley 16 toward the fixed section 318, i.e., from anintermediate position illustrated in solid lines in FIGS. 2 and 5 to aninner position illustrated in dashed lines at 44. Simultaneously withthis operation of the drive assembly 20, the drive assembly 26 isoperated to decrease the effective diameter of the drive pulley 18 bymoving the section 36 of the drive pulley 18 away from the fixed section40 of the drive pulley, i.e., from the intermediate position shown insolid lines in FIGS. 2 and 6 to the outer position indicated by dashedlines at 46, to thereby decrease the effective diameter of the drivepulley 18. In this manner an increase in the diameter of the drivepulley 16 is offset by a decrease in the diameter of the drive pulley 18so that the tension in the drivebelt 20 remains substantially constant.Of course, increasing the effective diameter of the drive pulley l6 anddecreasing the effective diameter of the drive pulley 18 results in thespeed of rotation of the output shaft 14 being increased relative to thespeed of rotation of the input shaft 12.

Similarly, the effective diameter of the drive pulley 16 can bedecreased by operating the drive assembly 24 to move the section 34outwardly to a position indicated in dashed lines at 50 in FIGS. 2 and5. Simultaneously therewith, the drive assembly 26 is operated to movethe section 36 of the drive pulley 18 to an inner position, indicated indashed lines at 52 in FIGS. 2 and 6, to thereby increase the effectivediameter of the drive pulley 18. Of course, increasing the effectivediameter of the drive pulley 18 while decreasing the effective diameterof the drive pulley 16 slows the speed of rotation of the output shaft14 relative to the speed of rotation of the input shaft 12.

The extent of movement of the movable sections 34 and 36 relative to thefixed sections 38 and 40 determines the extent to which the effectivediameters of the drive pulleys 16 and 18 are varied. Since the driveassemblies 24 and 26 are operated by the control assembly 30 to effectmovement of the sections 34 and 36 of the drive pulleys 16 and 18, theextent of movement of the pulley sections is determined by the durationof operation of the control assembly 30. Of course, the greater thechange in the effective diameters of the drive pulleys 16 and 18 thegreater is the change in the speed of rotation of the output member 14relative to the speed of rotation of the input member 12.

To prevent skewing or deflecting of the drivebelt 20, the movablesections 34 and 36 of the drive pulleys 16 and 18 are located onopposite sides of the drivebelt 20. When the movable section 34 of thedrive pulley 16 is moved inwardly to increase the effective diameter ofthe drive pulley 16 and the movable section 36 of the drive pulley 18 ismoved outwardly to decrease the effective diameter of the drive pulley18, the drivebelt 20 is shifted axially from the position shown in solidlines in H6. 2 to the position indicated in dashed lines at 56 in FIG.2. Since the effective diameter of the drive pulley 16 is increased byan amount which corresponds to the decrease in the effective diameter ofthe drive pulley 18, the sections 34 and 36 are moved axially throughthe same distance so that the drivebelt 20 is not skewed or cocked dueto the movement of the sections 34 and 36. Similarly, when the effectivediame ter of the drive pulley 16 is decreased and the effective diameterof the drive pulley 18 increased, the drivebelt 20 is shifted axially tothe position indicated in dashed lines at 58 in H6. 2 to prevent skewingor deflection of the drivebelt.

Upon receipt of a command signal, the control mechanism 30 operates bothof the drive assemblies 24 and 26 to simultaneously vary the effectivediameters of the drive pulleys 16 and 18 by amounts which are a functionof the command signal. The control assembly 30 includes a pair ofcontrol pulleys 62 and 64 (FIGS. 1 and 2) which are connected to thedrive assemblies 24 and 26, respectively. A main control pulley 68 isdrivingly connected with the control pulleys 62 and 64 by a control ortiming belt 70. Rotation of the main control pulley 68 drives the timingbelt 70 to rotate the control pulleys 62 and 64 and thereby operates thedrive assemblies 24 and 26. The timing belt 70 is advantageously of thecog type and meshes with teeth fonned on the control pulleys 62, 64 and68 to provide a positive drive from the main control pulley 68 to thecontrol pulleys 62 and 64.

The main drive pulley 68 is driven by a reversible servomotor 74 (FIG.3) of a servosystem 76 in response to a command signal from a suitablesensor or other device which provides a command signal when the speed ofrotation of the output shaft 14 is to be either increased or decreasedrelative to the speed of rotation of the input shaft 12. The servosystem76 is of a type which is well known per se and includes a conductor 80for transmitting command signals from the sensor to an error detector82. The error detector 82 is operable to compare the command signal witha feedback signal conducted over a lead 84 from a signal generator 86.

If the speed of the output shaft 14 is to be varied relative to thespeed of the input shaft 12, a command signal is transmitted to theerror detector 82. Upon receipt of the command signal, the errordetector 82 transmits a control or error signal which is amplified andeffects energization of the servomotor 74. Energization of theservomotor 74 rotates the main drive pulley 68 through a reduction geartrain 90. Rotation of the main control pulley 68 is transmitted by thedrivebelt 70 to the control pulleys 62 and 64 to operate the driveassemblies 24 and 26.

1f the servomotor 74 is operated in a first or forward direction, thecontrol pulleys 62 and 64 are rotated in a first direction to operatethe drive assemblies 24 and 26 to increase the effective diameter of thedrive pulley 16 and decrease the effective diameter of the drive pulley18. Conversely if the servomotor 74 is operated in the reversedirection, the direction of rotation of the control pulley 62 and 64 isreversed to operate the drive assemblies 24 and 26 to decrease theeffective diameter of the drive pulley 16 and increase the effectivediameter of the drive pulley 18. Thus, depending upon the command signalreceived by the error detector 82, the servomotor 74 is operable ineither of two directions to effect either an increase or a decrease inthe speed of rotation of the output shaft 14 relative to the speed ofrotation of the input shaft 12.

The signal generator 86, which generates the feedback signal, is alsodriven by the gear train 90. Therefore, the feedback signal transmittedto the error detector 82 varies with variations in the angular positionof the control pulleys 62, 64 and 68. As the angular position of thecontrol pulleys 62, 64 and 68 changes, that is as the control pulleysrotate, the drive assemblies 24 and 26 are driven to vary the effectivediameters of the drive pulleys 16 and 18 by an amount which is directlyproportional to the extent of angular movement of the control pulleys62, 64 and 68. Therefore, the feedback signal from the signal generator86 varies as a function of variations in the effective diameters of thedrive pulleys 16 and 18 and as a function of variations in the speed ofthe output member 14 relative to the speed of the input member 12. Theuse of the cog-type timing belt 70 for driving the control pulleys 62,64 and 68 ensures that there is no slippage between the drivebelt andthe control pulleys so that the feedback signal from the signalgenerator 86 properly indicates the extent of rotational movement of thecontrol pulleys 62 and 64 and variations in the effective diameters ofthe drive pulleys 16 and 18. Although many different types of signalgenerators 86 can be used, in the illustrated embodiment of theinvention the signal generator 86 is a known transformer assembly.

The gear train 90 is of the speed-reducing type so that a relativelylarge angular movement of a pinion gear 94 which is connected to a driveshaft 96 of the servomotor 74, results in a relatively small angularmovement or rotation of the main control pulley 68. Rotational movementof the pinion gear 94 is transmitted to an idler shaft 100 by a gear 102(see FIGS. 3 and 4) which is in meshing engagement with the pinion gear94. Rotation of the shaft 100 is in turn transferred by a pinion gear104 to a relatively large gear 106 and a gear shaft 108. This rotationof the gear shaft 108 is transmitted by a pinion gear 110 to a gear 112which is fixedly mounted on a shaft 114. Rotation of the shaft 114rotates a pinion gear 116 and a main drive gear 118 which is fixedlyconnected to a shaft 120. One end portion of the shaft 120 drives thesignal generator 86. The opposite end portion of the shaft 120 isfixedly connected to the main control pulley 68. Therefore, rotation ofthe shaft 120 drives the signal generator to an extent which correspondsto the extent of angular or rotational movement of the main controlpulley 68.

The two drive assemblies 24 and 26 (see FIGS. 5 and 6) are operable uponrotation of the control pulleys 62 and 64 to vary the effectivediameters of the drive pulleys 16 and 18. Although the two driveassemblies 24 and 26 differ somewhat from each other, they have manycommon features. Thus, the drive assemblies 24 and 26 both includeexternally threaded shafts and 132 which are parallel to each other andare fixedly connected at one end portion to the control pulleys 62 and64, respectively. Connector assemblies 136 and 138 connect the oppositeends of the shafts 130 and 132 with the movable sections 34 and 36 ofthe associated drive pulleys 16 and 18. The connector assemblies 136 and138 enable the shafts 130 and 132 to rotate relative to the movablepulley sections 34 and 36 while retaining the shafts 130 and 132 againstaxial movement relative to the associated pulley sectrons.

Internally threaded nuts 142 and 144 (FlGS. 5 and 6) cooperate with theexternally threaded shafts 130 and 132, respectively, and are retainedagainst axial movement by a frame assembly 148. Internal threadconvolutions and 152 on the nuts 142 and 144 are connected with externalthread convolutions 154 and 156 on the shafts 130 and 132 in a knownmanner by suitable balls or bearings 158. The thread convolutions 150through 156 have the same pitch and direction of slope. Therefore, uponrotation of the control pulleys 62 and 64 by the timing belt 70, theshafts 130 and 132 are rotated in the same direction (see FIG. 1) andthe interaction between the external thread convolutions 154 and 156,the balls 158 and the internal thread convolutions 150 and 152 resultsin the shafts being moved axially relative to the nuts 142 and 144 andthe frame 148 for equal distances in the same direction. This axialmotion of the shafts 130 and 132 is transmitted by the connectorassemblies 136 and 138 to the movable sections 34 and 36 of the drivepulleys 16 and 18 to efi'ect substantially equal variations in theeffective diameters of the drive pulleys.

If the effective diameter of the drive pulley 16 is to be increased andthe effective diameter of the drive pulley 18 decreased, the maincontrol pulley 68 is rotated in a clockwise direction as viewed in FIG.1 by operation of the servomotor 74. The two control pulleys 62 and 64and associated shafts 130 and 132 are also rotated in a clockwisedirection as viewed in FIG. 1. This rotation of the shafts 130 and 132relative to the nuts 142 and 144 causes the shafts and the controlpulleys 62 and 64 to be moved axially toward the left as viewed in FIGS.5 and 6. The leftward movement of the shafts 130 and 132 (as viewed inFIGS. 5 and 6) causes the movable section 34 of the drive pulley 16 tomove toward the associated fixed section 38 to thereby increase theeffective diameter of the drive pulley 16. Similarly, the leftwardmovement of the shaft 132 moves the movable section 36 of the drivepulley 18 away from the associated fixed pulley section 40 to therebydecrease the effective diameter of the drive pulley 18. Since themovable pulley sections 34 and 36 are both moved for substantially thesame distance toward the left (as viewed in FIGS. 5 and 6), thedrivebelt 20 is shifted toward the position indicated in dashed lines at56 in FIG. 2 without skewing or cocking of the drivebelt.

Conversely, when the main control pulley 68 is rotated in acounterclockwise direction (as viewed in FIG. 1) by operation of theservomotor 74, the control pulleys 62 and 64 and shafts 130 and 132 arerotated in a counterclockwise direction. This counterclockwise rotationof the shafts 130 and 132 results in an interaction with the nuts 142and 144 to move the shafts toward the right as viewed in FIGS. 5 and 6Therefore, the movable section 34 of the drive pulley 16 is moved awayfrom the associated fix'ed section 38 of the drive pulley 16 to therebydecrease its effective diameter. Similarly, the movable section 36 ofthe drive pulley 18 is moved toward the associated fixed section 40 tothereby increase the effective diameter of the drive pulley 18.

Although the drive assemblies 24 and 26 are similar in many respects,they differ somewhat in the precise manner in which the shafts 130 and132 and movable pulley sections 34 and 36 are interconnected. Theconnector assembly 136 (FIG. 5) for operatively connecting the shaft 130to the movable section 34 of the drive pulley 16 includes an innerannular member 164 which is fixedly connected by a suitable nut and keyarrangement 166 to one end of the shaft 130. A bearing assembly 1711enables the inner annular member 164 to rotate relative to an outerannular member 174 which is splined or keyed to a casing or housing 176for axial movement relative thereto. Upon axial movement of the shaft130 and inner annular member 164, the bearing assembly 170 moves theouter annular member 174 axially relative to the housing 176 and fixedpulley section 38.

The movable pulley section 34 is fixedly mounted on a slide block 178which is in turn connected by a bolt 180 to the outer annular member174. Therefore, upon axial movement of the outer annular member 174 withthe shaft 130, the slide block 178 is moved in the same direction tomove the movable section 34 of the drive pulley 16 relative to the fixedsection 38 of the drive pulley. This axial movement of the slide block178 is guided by a spline or key 186 formed on a sleeve 188 which isfixedly connected to the input shaft 12. The sleeve 188 is retainedagainst rotation relative to the input shaft 12 by a suitable keyarrangement 190 and is retained against axial movement relative to theinput shaft 12 by a bolt 192 which secures an end plate 194 to the inputshaft 12. It should be noted that the end plate 194 is integrally formedwith the housing 176 so that the housing rotates with the drive pulley16. v

The fixed pulley section 38 is secured to the sleeve 188 by an annularsupport block 200. The annular support block 206 is bolted to aconnector ring 202 which extends into a recess in the sleeve 188 toretain the support block 200 against axial movement relative to thesleeve. A clamp assembly 206 engages the input shaft 12 and sleeve 188to further retain the sleeve against axial movement relative to theinput shaft 12. Since both sections of the drive pulley 16 are securedagainst rotation relative to the sleeve 188, they are rotated therewithupon rotation of the input shaft 12.

The housing 176 encloses the nut 142 and the threaded portion 154 of theshaft 130. To facilitate relative movement between the threaded shaftand nut 142, the housing 176 is at least partially filled with oil orother lubricating fluid. This lubricating fluid is retained by seals 212and 214 in a cavity 217 defined by the housing 176. Rotation of thehousing 176 relative to the nut is facilitated by a pair of bearingassemblies 216 and 218 which are disposed between the housing 176 and asupport member 222. The bearing assemblies 216 and 218 retain thehousing 176 against axial movement relative to the support member 222.The support member 222 is rotatably supported by the frame 148 whilebeing retained against axial movement relative to the frame. A threadedend portion 223 of the nut 142 engages internal threads on the supportmember 222 and is held against rotation relative thereto by a setscrew224. It should be noted that the nut 142 and support member 222 can berotated together relative to the frame assembly 148. However, they areheld against axial movement relative to the frame assembly 148.

The connector assembly 138 (FIG. 6) for operatively connecting the shaft132 to the movable section 36 of the drive pulley 18 includes an innerannular member 230 which is fixedly connected by a suitable nut and keyarrangement 232 to one end of the shaft 132. A bearing assembly 234enables the inner annular member 230 to rotate relative to an outerannular member 236 which is splined or keyed to a casing or housing 238for axial movement relative: thereto. Accordingly, upon axial movementof the shaft 132 and inner annular member 230, the bearing assembly 234moves the outer annular member 236 axially relative to the housing 238and fixed pulley section 40.

The movable pulley section 36 is fixedly mounted on a slide block 240which is in turn connected by a bolt 242 to the outer annular member236. Therefore, upon axial movement of the outer annular member 236 withthe shaft 132, the slide block 240 is moved in the same direction tomove the movable section 36 of the drive pulley 18 relative to the fixedsection 411 of the drive pulley. This axial movement of the slide block240 is guided by a spline or key 243 formed on a sleeve 244 which isfixedly connected to the output shaft 14. The sleeve 244 is retainedagainst rotation relative to the output shaft 14 by a suitable keyarrangement 245 and is retained against axial movement relative to theoutput shaft 14 by a bolt 246 which secures an end plate 247 to theoutput shaft 14.

The fixed pulley section 411 is fixedly secured to the housing 238 whichis keyed or splined at 248 to the sleeve 244. The housing 238 isretained against axial movement relative to the sleeve 244 by aconnector ring 249. A clamp assembly 250 engages the output shaft 14 andsleeve 244 to further retain the sleeve against axial movement relativeto the output shaft 14. Since both sections of the drive pulley 18 aresecured against rotation relative to the sleeve 244, they are rotatedtherewith upon rotation of the output shaft 14.

The housing 238 encloses the nut 144 and the threaded portion 156 of theshaft 132. To facilitate relative movement between the threaded shaft132 and nut 144, the housing 238 is at least partially filled with oilor other lubricating fluid. This lubricating fluid is retained by seals252 and 254 in a cavity 256 defined by the housing 238. Rotation of thehousing 238 relative to the nut is facilitated by a pair of bearingassemblies 260 and 262 which are disposed between the housing 238 and asupport member 264. The bearing assemblies 260 and 262 retain thehousing 238 against axial movement relative to the support member 264.The support member 264 is rotatably supported by the frame 148 whilebeing retained against axial movement relative to the frame. A threadedend portion 265 of the nut 144 engages internal threads on the supportmember 264 and is held against rotation relative thereto by a setscrew266. It should be noted that the nut 144 and support member 264 can berotated together relative to the frame assembly 148. However, they areheld against axial movement relative to the frame assembly 148.

When the servomotor 74 is energized to drive the main control pulley 68,the control pulleys 62 and 64 are associated shafts 130 and 132 arerotated and move axially relative to the frame 148 by the interactionbetween the shafts 130 and 132 and the nuts 142 and 144. To preventskewing or deflection of the timing belt 70, the timing belt is movedaxially relative to the main control pulley 68 which is held againstaxial movement relative to the frame 148 by the shaft 120 (FIG. 3). Toenable the timing belt 70 to be moved relative to the main controlpulley 68, the main control pulley has a toothed drive surface 314 whichis generally cylindrical in configuration and has an axial extent whichis greater than the width of the timing belt 70 (see FIG. 2). Therefore,when the control pulleys 62 and 64 are moved axially relative to theframe 148 with the shafts 130 and 132, the timing belt 70 is slidaxially along the driving surface 314 to prevent the belt from beingskewed or deflected. It should be noted that the timing belt 70 is ofthe cog type and has sections or teeth which interact with the teeth onthe driving surface 314 of the main control pulley 68 so that thedriving relationship is maintained between the main control pulley 68and timing belt 70 during this axial movement of the timing belt andwithout relative rotation between the main control pulley and the timingbelt.

During operation of the transmission assembly 10, the main drive belt 20tends to stretch or otherwise increase in length. Stretching of the maindrivebelt 20 reduces the tension in the drivebelt and the pressureexerted by the drivebelt against the drive pulleys 16 and 18. As thedrivebelt 20 slackens due to a stretching of the drivebelt, there is anincreasing tendency for the drivebelt20 to slip relative to the pulleys16 and 18. Of course, this will substantially impair the ability of thedrivebelt 20 to transmit forces from the input member 12 to the outputmember 14. Therefore, a belt stretch compensator or antibacklashassembly 320 (FIG. 1) is provided to take up any slack resulting from astretching or other increase in the effective length of the maindrivebelt 20.

The compensator assembly 320 urges both of the movable pulley sections34 and 36 toward the associated fixed pulley sections 38 and 40 tothereby increase the effective diameters of the pulleys 16 and 18 inresponse to an increase in the effective length of the main drivebelt20. This increase in the effective diameters of the pulleys 16 and 18takes up any slack in the drivebelt 20 to maintain the drivebelt taut.The compensator assembly 320 includes a biasing spring assembly 324(FIG. 1) which applies a constant biasing force to the nuts 142 and 144to tend to rotate them relative to the shafts 130 and 132 (FIGS. and 6).This biasing force tends to rotate the nut 142 in a clockwise direction,viewed from the right-hand end of the shaft 130, and to rotate the nut144 in a counterclockwise direction, as viewed from the right-hand endof the shaft 132.

When the drivebelt is extending tautly between the pulleys l6 and 18,the tension forces in the drivebelt 20 offset the biasing forces appliedto the nuts 142 and 144 by the spring assembly 324. However if thetension in the drivebelt 20 is reduced due to an increase in theeffective length of the drivebelt, the biasing forces on the nuts 142and 144 cause them to rotate relative to the shafts 130 and 132. Sincethe nuts 142 and 144 are held against axial movement relative to theframe 148, rotation of the nuts causes them to move the shaft 130 to theleft as viewed in FIG. 5 and to move the shaft 132 toward the right asviewed in FIG. 6. As was previously explained, this movement of theshafts 130 and 132 increases the effective diameters of the drivepulleys 6 and 18. Of course, the increase in the effective diameters ofthe drive pulleys l6 and 18 takes up the slack resulting from astretching of the belt 20 to thereby maintain tension in the belt 20 andfrictional pressure of the belt against the pulleys 16 and 18.

The biasing spring assembly 324 includes a connector rod 328 which ispivotally connected to an outwardly projecting arm 330 on a connectorring 332 (See FIG. 6) which is secured to the support member 264 for thenut 144. The connector rod 328 extends through and is slidable relativeto a support block 336. A biasing spring 338 extends between the supportblock 336 and in an adjustable nut assembly 340 which is connected tothe outer end of the connector rod 328. The biasing spring 338 exerts aleftward (as viewed in FIG. 1) force on the nut assembly 340 to tend torotate the arm 330 and connector member 332 in a generallycounterclockwise direction as viewed in FIG. 1. This biasing force tendsto rotate the nut 144 relative to the shaft 132 in a direction to causethe shaft to be moved toward the right as viewed in FIG. 6. Of course,this rightward movement of the shaft 132 moves the section 36 of thedrive pulley 18 toward the fixed section 40 of the drive pulley toincrease the effective diameter of the pulley.

The nut 142 must be biased in the opposite direction from the nut 144 totend to urge the movable section 34 of the drive pulley 16 toward thefixed section 38 in order to increase the effective diameter of thedrive pulley. To accomplish this, a connector link 344 is connected atone end to a second arm 346 which extends outwardly toward the left (asviewed in FIG. 1) from the connector member 332. The other end of thelink 344 is pivotally connected to an arm 350 which extends outwardlytoward the right (as viewed in FIG. 1) from a connector member 352 (FIG.5). Therefore, the link 344 transmits biasing forces in a generallydownward direction to the connector member 352 to thereby tend to rotatethe nut 142 in a direction opposite from that which the biasing springassembly 324 tends to rotate the nut 144.

The single biasing spring 338 is operable to apply a biasing force toboth of the nuts 142 and 144. This biasing force tends to rotate thenuts 142 and 144 to effect an increase in the effective diameters of thepulleys 16 and 18 in response to an increase in the effective length ofthe drivebelt 20. In this manner, the belt stretch compensator assembly320 tends to maintain the tension in the drivebelt 20 substantiallyconstant even though the drivebelt may stretch during operation of thetransmission assembly 10. Of course, when the effective diameters of thepulleys 16 and 18 are increased, the speed of rotation of the outputmember 14 relative to the speed of rotation of the input member 12 willtend to change. Therefore, the sensor associated with the lead and errordetector 82 will provide a suitable command signal to operate the driveassemblies 24 and 26 to provide the desired drive ratio between theinput member 12 and output member 14 in the manner previously explained.

In view of the foregoing remarks, it can be seen that the transmissionassembly 10 includes a pair of variable diameter drive pulleys whoseeffective diameters can automatically be changed to vary the speed ofrotation of an output member 14 relative to the speed of rotation of aninput member 12 in response to a command signal. The command signal,conducted over the lead 80 to the error detector 82, effects operationof a reversible servomotor 74 to operate a pair of drive assemblies 24and 26 each of which is associated with one of the drive pulleys 16 and18. Operation of the drive assemblies 24 and 26 moves the sections ofone of the drive pulleys 16 or 18 together to increase the effectivediameter of this drive pulley and moves sections of the other drivepulley apart to decrease its effective diameter. A signal generator 86provides a feedback signal which varies with variations in the effectivediameters of the drive pulleys l6 and 18. The error detector 82 isoperable to effectively compare the feedback signals and command signalsand interrupts operation of the servomotor 74 when the effectivediameters of the drive pulleys l6 and 18 correspond to a predeterminedfunction of the command signal.

The compensator assembly 320 maintains the drivebelt 20 taut bycompensating for increases in the effective length of the drivebelt dueto stretching or other causes during operation of the transmissionassembly 10. The compensator assembly 320 accomplishes this byincreasing the effective diameters of drive pulleys 16 and 18 inresponse to an increase in the effective length of the drivebelt 20. Byincreasing the effective diameters of both of the drive pulleys 16 and18, any slack in the drivebelt 20 is taken up to thereby maintaintension in the drivebelt 20 to prevent slipping of the drivebeltrelative to the pulleys. When this occurs, the servosystem 76 isoperable in response to a command signal to maintain the desired driveratio between the input shaft 12 and output shaft 14.

Having described a specific, preferred embodiment of the invention, thefollowing is claimed:

1. A transmission assembly for automatically varying the speed of anoutput member relative to the speed of an input member in response to acommand signal, said transmission assembly comprising a first drivepulley operatively connected to one of the members and having aplurality of sections which are movable relative to each other to varythe effective diameter of said first drive pulley, a second drive pulleyoperatively connected to the other of the members, said second drivepulley including a plurality of sections which are movable relative toeach other, drivebelt means for operatively interconnecting said firstand second drive pulleys and for transmitting forces therebetween, drivemeans for effecting relative movement between said sections of saidfirst drive pulley to vary the effective diameter of said first drivepulley and to thereby vary the speed of said output member relative tothe speed of said input member, said drive means being operable toeffect relative movement between the sections of said second drivepulley simultaneously with the aforesaid movement between the sectionsof said first drive pulley, and control means for operating said drivemeans to vary the effective diameter of said first drive pulley as afunction of the command signal, said control means including motor meansfor operating said drive means in response to the command signal toeffect relative movement between said sections of said first drivepulley to thereby vary the effective diameter of said first drivepulley, signal generator means for providing a feedback signal whichvaries as a function of variations in the relative positions of saidsections of said first drive pulley, means responsive to said feedbackand command signals for interrupting operation of said motor means whenthe feedback signal is a predetermined function of the command signal, afirst control pulley mounted in a fixed relationship with its axis ofrotation and operatively connected to said motor means, a second controlpulley mounted for movement along its axis of rotation upon relativemovement between said sections of said first drive pulley, a thirdcontrol pulley mounted for movement along its axis of rotation uponrelative movement between said sections of said second drive pulley, anda control drivebelt extending around said control pulleys to drivinglyinterconnect said control pulleys, said first control pulley having adrive surface for engaging said control drivebelt, said drive surface ofsaid first control pulley having an axial extent which is greater thanthe width of said control drivebelt to enable said control drivebelt tomove axially relative to said first control pulley upon movement of saidfirst and second control pulleys along their axes of rotation to therebytend to minimize deflection of said control drivebelt.

2. A transmission assembly as set forth in claim 1, further includingcompensator means for automatically effecting relative movement betweensaid sections of said first and second llli drive pulleys to increasethe effective diameters of said first and second drive pulleys inresponse to an increase in the effective length of said drivebelt means.

3. A transmission assembly for automatically varying the speed of anoutput member relative to the speed of an input member in response to acommand signal, said transmission assembly comprising a first drivepulley operatively connected to one of the members and having aplurality of sections which are movable relative to each other to varythe effective diameter of said first drive pulley, a second drive pulleyoperatively connected to the other of the members, said second drivepulley including a plurality of sections which are movable relative toeach other, drivebelt means for operatively interconnecting said firstand second drive pulleys and for transmitting forces therebetween, drivemeans for effecting relative movement between said sections of saidfirst drive pulley to vary the effective diameter of said first drivepulley and to thereby vary the speed of said output member relative tothe speed of said input member, said drive means being operable toeffect relative movement between the sections of said second drivepulley simultaneously with the aforesaid movement between the sectionsof said first drive pulley, and control means for operating said drivemeans to vary the effective diameter of said first drive pulley as afunction of the command signal, said control means including motor meansfor operating said drive means in response to the command signal toeffect relative movement between said sections of said first drivepulley to thereby vary the effective diameter of said first drivepulley, signal generator means for providing a feedback signal whichvaries as a function of variations in the relative positions of saidsections of said first drive pulley, means responsive to said feedbackand command signals for interrupting operation of said motor means whenthe feedback signal is a predetermined function of the command signal,and. a first drive assembly operatively connected to said first drivepulley and a second drive assembly operatively connected to said seconddrive pulley, said first and second drive assemblies each includinginter nally and externally threaded members which are operativelyconnected to said control means and one of said sections of anassociated one of said drive pulleys, said control means being operableto provide relative movement between said threaded members to move saidone of said sections of each of said drive pulleys relative to the othersection of each of said drive pulleys, said transmission assemblyfurther comprising compensator means for compensating for increases inthe efi'ective length of said drivebelt means by applying a biasingforce to rotate one of the members of each of said drive assemblies in adirection relative to the associated threaded member to increase theeffective diameter of said first and second drive pulleys.

i. A transmission assembly as set forth in claim 3 wherein one of saidsections of said first drive pulley is movable axially relative to theother section of said first drive pulley and is disposed on one side ofsaid drivebelt, and one of said sections of said second drive pulley ismovable axially relative to the other section of said second drivepulley and is disposed on a side of said drivebelt opposite from saidone side.

5. A transmission assembly for varying the speed of an output memberrelative to the speed of an input member, said transmission assemblycomprising a first drive pulley operatively connected to one of themembers and having a plurality of sections which are movable relative toeach other to vary the effective diameter of said first drive pulley, asecond drive pulley operatively connected to the other of the membersand including a plurality of sections which are movable relative to eachother, a drivebelt extending in tension between said first and seconddrive pulleys to transmit forces therebetween, drive means forselectively effecting relative movement between said sections of saidfirst drive pulley in a direction toward each other and in a directionaway from each other to selectively increase and decrease the effectivediameter of said first drive pulley and to thereby vary the speed ofsaid output member relative to the speed of said input member, saiddrive means being selectively operable to effect relative movementbetween the sections of said second drive pulley in a direction towardeach other and in a direction away from each other to selectivelyincrease and decrease the effective diame ter of said second drivepulley while said drive means simultaneously therewith effects theaforesaid movement between the sections of said first drive pulley, andcompensator means for automatically effecting relative movement betweensaid sections of said first drive pulley in a direction toward eachother in response to an increase in the effective length of saiddrivebelt and for simultaneously therewith effecting relative movementof said sections of said second drive pulley toward each other inresponse to an increase in the effective length of said drivebelt tomaintain the tension in said drivebelt by simultaneously increasing theeffective diameters of both said first and second drive pulleys.

6. A transmission assembly as set forth in claim wherein saidcompensator means includes spring means operatively connected with saiddrive means for applying a biasing force through said drive means to atleast one of said sections of said first drive pulley to thereby urgesaid one section toward the other section of said first drive pulley andfor applying a biasing force through said drive means to at least one ofsaid sections of said second drive pulley to thereby urge said onesection of said second drive pulley toward the other section of saidsecond drive pulley.

7. A transmission assembly as set forth in claim 5 wherein one of saidsections of said first drive pulley is movable axially relative to theother section of said first drive pulley and is disposed on one side ofsaid drivebelt, and one of said sections of said second drive pulley ismovable axially relative to the other section of said second drivepulley and is disposed on a side of said drivebelt opposite from saidone side.

8. A transmission assembly for automatically varying the speed of anoutput member relative to the speed of an input member in response to anelectrical command signal, said transmission assembly comprising a firstdrive pulley operatively connected to one of the members and having aplurality of sections which are movable relative to each other to varythe effective diameter of said first drive pulley, a second drive pulleyoperatively connected to the other of the members, drivebelt means foroperatively interconnecting said first and second drive pulleys and fortransmitting forces therebetween, drive means for effecting relativemovement between said sections of said first drive pulley to vary theeffective diameter of said first drive pulley and to thereby vary thespeed of said output member relative to the speed of said input member,and control means for activating said drive means to vary the effectivediameter of said first drive pulley as a function of the electricalcommand signal, said control means including electric motor meansoperable between a deenergized condition and an energized condition inwhich said electric motor means is effective to operate said drive meansto vary the effective diameter of said first drive pulley, means forconducting an electrical command signal to said electric motor means toeffect operation of said electric motor means from the deenergizedcondition to the energized condition to vary the effective diameter ofsaid first drive pulley in response to said electrical command signal,said electrical command signal having a characteristic indicative of apredetermined diameter of said first drive pulley, a signal generatormeans for providing an electrical feedback signal which varies as afunction of variations in the relative positions of said sections ofsaid first drive pulley, and means responsive to said feedback andcommand signals for deenergizing said electric motor means when theelectrical feedback signal is a predetermined function of the electricalcommand signal.

9. A transmission assembly as set forth in claim 8 wherein said controlmeans includes a first control pulley operatively connected to saidelectric motor means, a second control pulley mounted for rotation abouta common axis with said first drive pulley, a third control pulleymounted for rotation about a common axis with said second drive pulley,and a control drivebelt extending around said control pulleys todrivingly interconnect said control pulleys.

10. A transmission assembly as set forth in claim 9 wherein said seconddrive pulley includes a plurality of sections which are movable relativeto each other, said drive means being operable to effect relativemovement between the sections of said second drive pulley simultaneouslywith the aforesaid movement between the sections of said first drivepulley.

11. A transmission assembly for varying the speed of an out put memberrelative to the speed of an input member, said transmission assemblyincluding a first drive pulley operatively connected to said inputmember for rotation therewith and including a pair of sections mountedfor axial movement relative to each other to vary the effective diameterof said first drive pulley, a second drive pulley operatively connectedto said output member for rotation therewith and including a pair ofsections mounted for axial movement relative to each other to vary theeffective diameter of said second drive pulley, a main drivebeltextending around said first and second drive pulleys to therebyinterconnect said first and second drive pulleys, first drive meansoperable in a first direction to move said sections of said first drivepulley toward each other to increase the effective diameter of saidfirst drive pulley and operable in a second direction to move saidsections of said first drive pulley away from each other to decrease theeffective diameter of said first drive pulley, second drive meansoperable in a first direction to move said sections of said second drivepulley toward each other to increase the effective diameter of saidsecond drive pulley and operable in a second direction to move saidsections of said second drive pulley away from each other to decreasethe effective diameter of said second drive pulley, and control meansfor operating said first and second drive means to vary the effectivediameters of said first and second drive pulleys in response to acommand signal, said control means including a first control pulleyoperatively connected to said first drive means, a second control pulleyoperatively connected to said second drive means, a main control pulley,control belt means extending around said control pulleys to therebydrivingly interconnect said control pulleys, said main control pulleybeing rotatable in one direction to effect operation of said first drivemeans in its first direction to increase the effective diameter of saidfirst drive pulley and to simultaneously therewith effect operation ofsaid second drive means in its second direction to decrease theeffective diameter of said second drive pulley, said main control pulleybeing rotatable in another direction opposite to said one direction toeffect operation of said first drive means in its second direction todecrease the effective diameter of said first drive pulley and tosimultaneously therewith efiect operation of said second drive means inits first direction to increase the effective diameter of said seconddrive pulley, reversible servomotor means operatively connected to saidsecond main control pulley and operable in forward and reversedirections in response to the command signal to effect rotation of saidcontrol pulley and operation of said first and second drive means tothereby vary the effective diameters of said first and second drivepulleys in response to variations in the command signal, signalgenerator means operatively connected to said servomotor means forproviding a feedback signal which varies as a function of variations inthe effective diameters of said first and second drive pulleys uponoperation of said servomotor means, and means for interrupting operationof said servomotor means when the feedback signal is a predeterminedfunction of the command signal.

12. A transmission assembly as set forth in claim 11 wherein said firstdrive means includes a first externally threaded shaft operativelyconnected to said first control pulley, connector means for connectingone of said sections of said first drive pulley to said first shaft foraxial movement therewith and for enabling said first shaft to be rotatedrelative to said one section of said first drive pulley, firstinternally threaded nut means operatively connected to said first shaftfor effecting axial movement of said first shaft and said one section ofsaid first drive pulley relative to the other section of said firstdrive pulley upon rotation pf said first shaft to thereby vary the effective diameter of "said first drive pulley, said second drive meansincluding a second externally threaded shaft operatively connected tosaid second control pulley, connector means for connecting one of saidsections of said second drive pulley to said second shaft for axialmovement therewith and for enabling said second shaft to be rotatedrelative to said one section of said second drive pulley, secondinternally threaded nut means operatively connected to said second shaftfor effecting axial movement of said second shaft and said one sectionof said second drive pulley relative to the other section of said seconddrive pulley upon rotation of said second shaft to thereby vary theeffective diameter of said second drive pulley, said one section of saidfirst drive pulley being located on one side of said main drivebelt andsaid one section of said second drive pulley being located on theopposite side of said main drivebelt, said first and second shafts bothbeing rotatable in a one direction by said first and second controlpulleys upon operation of said servomotor means and rotation of saidmain control pulley in its one direction to operate said first drivemeans in its first direction and effect axial movement of said onesection of said first drive pulley toward said other section of saidfirst drive pulley to thereby increase the effective diameter of saidfirst drive pulley and to simultaneously therewith operate said seconddrive means in its second direction and effect movement of said onesection of said second drive pulley away from said other section of saidsecond drive pulley to thereby decrease the effective diameter of saidsecond drive pulley, said first and second shafts both being rotatablein another direction opposite to said one direction by said first andsecond control pulleys upon opera tion of said servomotor means androtation of said main control pulley in its other direction to operatesaid first drive means in its second direction and effect axial movementof said one section of said first drive pulley away from said othersection of said first drive pulley to thereby decrease the effectivediameter of said first drive pulley and to simultaneously therewithoperate said second drive means in its first direction and effectmovement of said one section of said second drive pulley toward saidother section of said second drive pulley to thereby increase theeffective diameter of said second drive pulley.

13. A transmission assembly as set forth in claim 12 further includingcompensator means for applying biasing forces to said first nut means ina direction to effect movement of said one section of said first drivepulley toward said other section of said first drive pulley and forsimultaneously therewith ap plying biasing forces to said second nutmeans in a direction to effect movement of said one section of saidsecond drive pulley toward said other section of said second drivepulley to thereby increase the effective diameters of said first andsecond drive pulleys in response to an increase in the effective lengthof said main drivebelt.

14. A transmission assembly as set forth in claim 12 wherein said firstand second nut means cooperate with said first and second shafts to movesaid first and second shafts and said first and second control pulleysin the same axial direction upon operation of said servomotor means androtation of said main control pulley, said main control pulley having agenerally cylindrical drive surface means for drivingly engaging saidcontrol belt means, said drive surface means having an axial extentwhich is greater than the width of said control belt means to enablesaid control belt means to be shifted axially relative to said maincontrol pulley upon axial movement of said first and second controlpulleys.

15. A transmission assembly for varying the speed of an output memberrelative to the speed of an input member, said transmission assemblycomprising a first drive pulley having a plurality of sections which aremovable relative to each other to vary the effective diameter of saidfirst drive pulley, a second drive pulley having a plurality of sectionswhich are movable relative to each other to vary the effective diameterof said second drive pulley, a drivebelt operatively interconnectingsaid first and second drive pulleys to transmit forces therebetween,drive means for effecting relative movement between said sections ofsaid first and second drive pulleys to vary the effective diameters ofsaid first and second drive pulleys and to thereby vary the speed ofsaid output member relative to the speed of said input member, andcontrol means for operating said drive means to vary the effectivediameters of said drive pulleys, said drive means including a firstdrive as sembly operatively connected to said first drive pulley and asecond drive assembly operatively connected to said second drive pulley,said first and second drive assemblies each including internally andexternally threaded members which are operatively connected to saidcontrol means and at least one of said sections of an associated one ofsaid drive pulleys, said control means being operable in a firstdirection to provide relative rotation between said threaded members tomove said one of said sections of each of said drive pulleys relativethe other section of each of said drive pulleys to increase theeffective diameter of said first drive pulley and to simultaneouslytherewith decrease the effective diameter of said second drive pulley,said control means being operable in a second direction to providerelative rotation between said threaded members to move said one of saidsections of each of said drive pulleys relative to the other section ofeach of said drive pulleys to decrease the effective diameter of saidfirst drive pulley and to simultaneously therewith increase theeffective diameter of said second drive pulley, and compensator meansfor applying a biasing force tending to rotate one of the threadedmembers of each of said drive assemblies in such a direction relative tothe associated threaded member as to simultaneously increase theeffective diameters of both of said drive pulleys to thereby take up anyslack which may result from an increase in the effective length of saiddrivebelt.

116. A transmission assembly as set forth in claim 15 wherein saidcontrol means includes means responsive to a change in the speed of theoutput member upon an increase in the effective diameters of said firstand second drive pulleys for offsetting the change in speed of theoutput member by operating said drive means to vary the effectivediameters of said drive pulleys.

17. A transmission assembly as set forth in claim 6 wherein said meansresponsive to the change in speed of the output member includes motormeans for operating said drive means in response to a command signalindicative of a change in speed of the output member relative to apredetermined speed to thereby effect relative movement between saidsections of said drive pulleys, signal generator means for providing afeedback signal which varies as a function of variations in the relativepositions of said sections of said drive pulleys, and means responsiveto said feedback and command signals for interrupting operation of saidmotor means when said feedback signal is a predetermined function ofsaid command signal.

18. A transmission assembly for varying the speed of an output memberrelative to the speed of an input member, said transmission assemblyincluding a first drive pulley operatively connected to said inputmember for rotation therewith and including a pair of sections mountedfor axial movement relative to each other to vary the effective diameterof said first drive pulley, a second drive pulley operatively connectedto said output member for rotation therewith and including a pair ofsections mounted for axial movement relative to each other to vary theeffective diameter of said second drive pulley, a main drivebeltextending around said first and second drive pulleys to therebyinterconnect said first and second drive pulleys, first drive meansoperable in a first direction to move said sections of said first drivepulley toward each other to increase the effective diameter of saidfirst drive pulley and operable in a second direction to move saidsections of said first drive pulley away from each other to decrease theeffective diameter of said first drive pulley, said first drive meansincluding a first externally threaded shaft, connector means forconnecting one of said sections of said first drive pulley to said firstshaft for axial movement therewith and for enabling said first shaft tobe rotated relative to said one section of said first drive pulley,first internally threaded nut means operatively connected to said firstshaft for effecting axial movement of said first shaft and said onesection of said first drive pulley relative to the other section of saidfirst drive pulley upon rotation of said first shaft to thereby vary theeffective diameter of said first drive pulley, second drive meansoperable in a first direction to move said sections of said second drivepulley toward each other to increase the effective diameter of saidsecond drive pulley and operable in a second direction to move saidsections of said second drive pulley away from each other to decreasethe effective diameter of said second drive pulley, said second drivemeans including a second externally threaded shaft, connector means forconnecting one of said sections of said second drive pulley to saidsecond shaft for axial movement therewith and for enabling said secondshaft to be rotated relative to said one section of said second drivepulley, second internally threaded nut means operatively connected tosaid second shaft for effecting axial movement of said second shaft andsaid one section of said second drive pulley relative to the othersection of said second drive pulley upon rotation of said second shaftto thereby vary the effective diameter of said second drive pulley, saidone section of said first drive pulley being located on one side of saidmain drivebelt and said one section of said second drive pulley beinglocated on the opposite side of said main drivebelt whereby relativemovement between said sections of said first and second drive pulleysupon operation of said first and second drive means tends to shift saidmain drivebelt axially with a minimum of deflection of said maindrivebelt, and control means for operating said first and second drivemeans to vary the effective diameters of said first and second drivepulleys, said control means including a first control pulley connectedto said first externally threaded shaft, a second control pulleyconnected to said second externally threaded shaft, a main controlpulley, control belt means extending around said control pulleys tothereby drivingly interconnect said control pulleys, said main controlpulley being rotatable in a first direction to effect operation of saidfirst drive means in its first direction by rotating said firstexternally threaded shaft in one direction relative to said firstinternally threaded nut means to increase the effective diameter of saidfirst drive pulley by moving said one section of said first drive pulleytoward said other section of said first drive pulley and tosimultaneously therewith effect operation of said second drive means inits second direction by rotating said second externally threaded shaftin said one direction relative to said second internally threaded nutmeans to decrease the effective diameter of said second drive pulley bymoving said one section of said second drive pulley away from said othersection of said second drive pulley, said main control pulley beingrotatable in a second direction opposite to said first direction toeffect operation of said first drive means in its second direction byrotating said first externally threaded shaft in another directionrelative to said first internally threaded nut means to decrease theeffective diameter of said first drive pulley by moving said one sectionof said first drive pulley away from said other section of said firstdrive pulley and to simultaneously therewith effect operation of saidsecond drive means in its first direction by rotating said secondexternally threaded shaft in said other direction relative to saidsecond internally threaded nut means to increase the effective diameterof said second drive pulley by moving said one section of said seconddrive pulley toward said other section of said second drive pulley, andcompensator means operatively connected to said first and secondinternally threaded nut means for applying biasing forces thereto toeffect relative rotation between said threaded nut means and said shaftsto move said shafts in a direction to increase the effective diametersof first and second drive pulleys in response to the occurrence of slackin said main drivebelt to thereby take up the slac k.

19. A transmission assembly as set forth in claim 18 wherein saidcompensator means includes spring means operatively connected to saidfirst and second internally threaded nut means for applying biasingforces thereto urging said first and second externally threaded nutmeans into tight-engagement with said first and second shafts.

20. A transmission assembly as set forth in claim 18 wherein said maincontrol pulley has a generally cylindrical drive surface means fordrivingly engaging said control belt means, said drive surface meanshaving an axial extent which is greater than the width of said controlbelt means to enable said control belt means to be shifted axiallyrelative to said main control pulley upon axial movement of said firstand second control pulleys.

2 A transmission assembly as set forth in claim 18 wherein said controlmeans further includes motor means for rotating said main control pulleyin response to a command signal to thereby effect rotation of said firstand second control pulleys and operation of said first and second drivemeans to vary the effective diameters of said first and second drivepulleys, signal generator means for providing a feedback signal whichvaries as a function of variations in the relative positions of saidsections of said first and second drive pulleys, and means forinterrupting operation of said motor means when the feedback signal is apredetennined function of the command signal.

1. A transmission assembly for automatically varying the speed of anoutput member relative to the speed of an input member in response to acommand signal, said transmission assembly comprising a first drivepulley operatively connected to one of the members and having aplurality of sections which are movable relative to each other to varythe effective diameter of said first drive pulley, a second drive pulleyoperatively connected to the other of the members, said second drivepulley including a plurality of sections which are movable relative toeach other, drivebelt means for operatively interconnecting said firstand second drive pulleys and for transmitting forces therebetween, drivemeans for effecting relative movement between said sections of saidfirst drive pulley to vary the effective diameter of said first drivepulley and to thereby vary the speed of said output member relative tothe speed of said input member, said drive means being operable toeffect relative movement between the sections of said second drivepulley simultaneously with the aforesaid movement between the sectionsof said first drive pulley, and control means for operating said drivemeans to vary the effective diameter of said first drive pulley as afunction of the command signal, said control means including motor meansfor operating said drive means in response to the command signal toeffect relative movement between said sections of said first drivepulley to thereby vary the effective diameter of said first drivepulley, signal generator means for providing a feedback signal whichvaries as a function of variations in the relative positions of saidsections of said first drive pulley, means responsive to said feedbackand command signals for interrupting operation of said motor means whenthe feedback signal is a predetermined function of the command signal, afirst control pulley mounted in a fixed relationship with its axis ofrotation and operatively connected to said motor means, a second controlpulley mounted for movement along its axis of rotation upon relativemovement between said sections of said first drive pulley, a thirdcontrol pulley mounted for movement along its axis of rotation uponrelative movement between said sections of said second drive pulley, anda control drivebelt extending around said control pulleys to drivinglyinterconnect said control pulleys, said first controL pulley having adrive surface for engaging said control drivebelt, said drive surface ofsaid first control pulley having an axial extent which is greater thanthe width of said control drivebelt to enable said control drivebelt tomove axially relative to said first control pulley upon movement of saidfirst and second control pulleys along their axes of rotation to therebytend to minimize deflection of said control drivebelt.
 2. A transmissionassembly as set forth in claim 1, further including compensator meansfor automatically effecting relative movement between said sections ofsaid first and second drive pulleys to increase the effective diametersof said first and second drive pulleys in response to an increase in theeffective length of said drivebelt means.
 3. A transmission assembly forautomatically varying the speed of an output member relative to thespeed of an input member in response to a command signal, saidtransmission assembly comprising a first drive pulley operativelyconnected to one of the members and having a plurality of sections whichare movable relative to each other to vary the effective diameter ofsaid first drive pulley, a second drive pulley operatively connected tothe other of the members, said second drive pulley including a pluralityof sections which are movable relative to each other, drivebelt meansfor operatively interconnecting said first and second drive pulleys andfor transmitting forces therebetween, drive means for effecting relativemovement between said sections of said first drive pulley to vary theeffective diameter of said first drive pulley and to thereby vary thespeed of said output member relative to the speed of said input member,said drive means being operable to effect relative movement between thesections of said second drive pulley simultaneously with the aforesaidmovement between the sections of said first drive pulley, and controlmeans for operating said drive means to vary the effective diameter ofsaid first drive pulley as a function of the command signal, saidcontrol means including motor means for operating said drive means inresponse to the command signal to effect relative movement between saidsections of said first drive pulley to thereby vary the effectivediameter of said first drive pulley, signal generator means forproviding a feedback signal which varies as a function of variations inthe relative positions of said sections of said first drive pulley,means responsive to said feedback and command signals for interruptingoperation of said motor means when the feedback signal is apredetermined function of the command signal, and a first drive assemblyoperatively connected to said first drive pulley and a second driveassembly operatively connected to said second drive pulley, said firstand second drive assemblies each including internally and externallythreaded members which are operatively connected to said control meansand one of said sections of an associated one of said drive pulleys,said control means being operable to provide relative movement betweensaid threaded members to move said one of said sections of each of saiddrive pulleys relative to the other section of each of said drivepulleys, said transmission assembly further comprising compensator meansfor compensating for increases in the effective length of said drivebeltmeans by applying a biasing force to rotate one of the members of eachof said drive assemblies in a direction relative to the associatedthreaded member to increase the effective diameter of said first andsecond drive pulleys.
 4. A transmission assembly as set forth in claim 3wherein one of said sections of said first drive pulley is movableaxially relative to the other section of said first drive pulley and isdisposed on one side of said drivebelt, and one of said sections of saidsecond drive pulley is movable axially relative to the other section ofsaid second drive pulley and is disposed on a side of said drivebeltopposite from sAid one side.
 5. A transmission assembly for varying thespeed of an output member relative to the speed of an input member, saidtransmission assembly comprising a first drive pulley operativelyconnected to one of the members and having a plurality of sections whichare movable relative to each other to vary the effective diameter ofsaid first drive pulley, a second drive pulley operatively connected tothe other of the members and including a plurality of sections which aremovable relative to each other, a drivebelt extending in tension betweensaid first and second drive pulleys to transmit forces therebetween,drive means for selectively effecting relative movement between saidsections of said first drive pulley in a direction toward each other andin a direction away from each other to selectively increase and decreasethe effective diameter of said first drive pulley and to thereby varythe speed of said output member relative to the speed of said inputmember, said drive means being selectively operable to effect relativemovement between the sections of said second drive pulley in a directiontoward each other and in a direction away from each other to selectivelyincrease and decrease the effective diameter of said second drive pulleywhile said drive means simultaneously therewith effects the aforesaidmovement between the sections of said first drive pulley, andcompensator means for automatically effecting relative movement betweensaid sections of said first drive pulley in a direction toward eachother in response to an increase in the effective length of saiddrivebelt and for simultaneously therewith effecting relative movementof said sections of said second drive pulley toward each other inresponse to an increase in the effective length of said drivebelt tomaintain the tension in said drivebelt by simultaneously increasing theeffective diameters of both said first and second drive pulleys.
 6. Atransmission assembly as set forth in claim 5 wherein said compensatormeans includes spring means operatively connected with said drive meansfor applying a biasing force through said drive means to at least one ofsaid sections of said first drive pulley to thereby urge said onesection toward the other section of said first drive pulley and forapplying a biasing force through said drive means to at least one ofsaid sections of said second drive pulley to thereby urge said onesection of said second drive pulley toward the other section of saidsecond drive pulley.
 7. A transmission assembly as set forth in claim 5wherein one of said sections of said first drive pulley is movableaxially relative to the other section of said first drive pulley and isdisposed on one side of said drivebelt, and one of said sections of saidsecond drive pulley is movable axially relative to the other section ofsaid second drive pulley and is disposed on a side of said drivebeltopposite from said one side.
 8. A transmission assembly forautomatically varying the speed of an output member relative to thespeed of an input member in response to an electrical command signal,said transmission assembly comprising a first drive pulley operativelyconnected to one of the members and having a plurality of sections whichare movable relative to each other to vary the effective diameter ofsaid first drive pulley, a second drive pulley operatively connected tothe other of the members, drivebelt means for operativelyinterconnecting said first and second drive pulleys and for transmittingforces therebetween, drive means for effecting relative movement betweensaid sections of said first drive pulley to vary the effective diameterof said first drive pulley and to thereby vary the speed of said outputmember relative to the speed of said input member, and control means foractivating said drive means to vary the effective diameter of said firstdrive pulley as a function of the electrical command signal, saidcontrol means including electric motor means operable between adeenergized condition and an energized condition in which said electricmotor means is effective to operate said drive means to vary theeffective diameter of said first drive pulley, means for conducting anelectrical command signal to said electric motor means to effectoperation of said electric motor means from the deenergized condition tothe energized condition to vary the effective diameter of said firstdrive pulley in response to said electrical command signal, saidelectrical command signal having a characteristic indicative of apredetermined diameter of said first drive pulley, a signal generatormeans for providing an electrical feedback signal which varies as afunction of variations in the relative positions of said sections ofsaid first drive pulley, and means responsive to said feedback andcommand signals for deenergizing said electric motor means when theelectrical feedback signal is a predetermined function of the electricalcommand signal.
 9. A transmission assembly as set forth in claim 8wherein said control means includes a first control pulley operativelyconnected to said electric motor means, a second control pulley mountedfor rotation about a common axis with said first drive pulley, a thirdcontrol pulley mounted for rotation about a common axis with said seconddrive pulley, and a control drivebelt extending around said controlpulleys to drivingly interconnect said control pulleys.
 10. Atransmission assembly as set forth in claim 9 wherein said second drivepulley includes a plurality of sections which are movable relative toeach other, said drive means being operable to effect relative movementbetween the sections of said second drive pulley simultaneously with theaforesaid movement between the sections of said first drive pulley. 11.A transmission assembly for varying the speed of an output memberrelative to the speed of an input member, said transmission assemblyincluding a first drive pulley operatively connected to said inputmember for rotation therewith and including a pair of sections mountedfor axial movement relative to each other to vary the effective diameterof said first drive pulley, a second drive pulley operatively connectedto said output member for rotation therewith and including a pair ofsections mounted for axial movement relative to each other to vary theeffective diameter of said second drive pulley, a main drivebeltextending around said first and second drive pulleys to therebyinterconnect said first and second drive pulleys, first drive meansoperable in a first direction to move said sections of said first drivepulley toward each other to increase the effective diameter of saidfirst drive pulley and operable in a second direction to move saidsections of said first drive pulley away from each other to decrease theeffective diameter of said first drive pulley, second drive meansoperable in a first direction to move said sections of said second drivepulley toward each other to increase the effective diameter of saidsecond drive pulley and operable in a second direction to move saidsections of said second drive pulley away from each other to decreasethe effective diameter of said second drive pulley, and control meansfor operating said first and second drive means to vary the effectivediameters of said first and second drive pulleys in response to acommand signal, said control means including a first control pulleyoperatively connected to said first drive means, a second control pulleyoperatively connected to said second drive means, a main control pulley,control belt means extending around said control pulleys to therebydrivingly interconnect said control pulleys, said main control pulleybeing rotatable in one direction to effect operation of said first drivemeans in its first direction to increase the effective diameter of saidfirst drive pulley and to simultaneously therewith effect operation ofsaid second drive means in its second direction to decrease theeffective diameTer of said second drive pulley, said main control pulleybeing rotatable in another direction opposite to said one direction toeffect operation of said first drive means in its second direction todecrease the effective diameter of said first drive pulley and tosimultaneously therewith effect operation of said second drive means inits first direction to increase the effective diameter of said seconddrive pulley, reversible servomotor means operatively connected to saidsecond main control pulley and operable in forward and reversedirections in response to the command signal to effect rotation of saidcontrol pulley and operation of said first and second drive means tothereby vary the effective diameters of said first and second drivepulleys in response to variations in the command signal, signalgenerator means operatively connected to said servomotor means forproviding a feedback signal which varies as a function of variations inthe effective diameters of said first and second drive pulleys uponoperation of said servomotor means, and means for interrupting operationof said servomotor means when the feedback signal is a predeterminedfunction of the command signal.
 12. A transmission assembly as set forthin claim 11 wherein said first drive means includes a first externallythreaded shaft operatively connected to said first control pulley,connector means for connecting one of said sections of said first drivepulley to said first shaft for axial movement therewith and for enablingsaid first shaft to be rotated relative to said one section of saidfirst drive pulley, first internally threaded nut means operativelyconnected to said first shaft for effecting axial movement of said firstshaft and said one section of said first drive pulley relative to theother section of said first drive pulley upon rotation of said firstshaft to thereby vary the effective diameter of said first drive pulley,said second drive means including a second externally threaded shaftoperatively connected to said second control pulley, connector means forconnecting one of said sections of said second drive pulley to saidsecond shaft for axial movement therewith and for enabling said secondshaft to be rotated relative to said one section of said second drivepulley, second internally threaded nut means operatively connected tosaid second shaft for effecting axial movement of said second shaft andsaid one section of said second drive pulley relative to the othersection of said second drive pulley upon rotation of said second shaftto thereby vary the effective diameter of said second drive pulley, saidone section of said first drive pulley being located on one side of saidmain drivebelt and said one section of said second drive pulley beinglocated on the opposite side of said main drivebelt, said first andsecond shafts both being rotatable in a one direction by said first andsecond control pulleys upon operation of said servomotor means androtation of said main control pulley in its one direction to operatesaid first drive means in its first direction and effect axial movementof said one section of said first drive pulley toward said other sectionof said first drive pulley to thereby increase the effective diameter ofsaid first drive pulley and to simultaneously therewith operate saidsecond drive means in its second direction and effect movement of saidone section of said second drive pulley away from said other section ofsaid second drive pulley to thereby decrease the effective diameter ofsaid second drive pulley, said first and second shafts both beingrotatable in another direction opposite to said one direction by saidfirst and second control pulleys upon operation of said servomotor meansand rotation of said main control pulley in its other direction tooperate said first drive means in its second direction and effect axialmovement of said one section of said first drive pulley away from saidother section of said first drive pulley to thereby decrease tHeeffective diameter of said first drive pulley and to simultaneouslytherewith operate said second drive means in its first direction andeffect movement of said one section of said second drive pulley towardsaid other section of said second drive pulley to thereby increase theeffective diameter of said second drive pulley.
 13. A transmissionassembly as set forth in claim 12 further including compensator meansfor applying biasing forces to said first nut means in a direction toeffect movement of said one section of said first drive pulley towardsaid other section of said first drive pulley and for simultaneouslytherewith applying biasing forces to said second nut means in adirection to effect movement of said one section of said second drivepulley toward said other section of said second drive pulley to therebyincrease the effective diameters of said first and second drive pulleysin response to an increase in the effective length of said maindrivebelt.
 14. A transmission assembly as set forth in claim 12 whereinsaid first and second nut means cooperate with said first and secondshafts to move said first and second shafts and said first and secondcontrol pulleys in the same axial direction upon operation of saidservomotor means and rotation of said main control pulley, said maincontrol pulley having a generally cylindrical drive surface means fordrivingly engaging said control belt means, said drive surface meanshaving an axial extent which is greater than the width of said controlbelt means to enable said control belt means to be shifted axiallyrelative to said main control pulley upon axial movement of said firstand second control pulleys.
 15. A transmission assembly for varying thespeed of an output member relative to the speed of an input member, saidtransmission assembly comprising a first drive pulley having a pluralityof sections which are movable relative to each other to vary theeffective diameter of said first drive pulley, a second drive pulleyhaving a plurality of sections which are movable relative to each otherto vary the effective diameter of said second drive pulley, a drivebeltoperatively interconnecting said first and second drive pulleys totransmit forces therebetween, drive means for effecting relativemovement between said sections of said first and second drive pulleys tovary the effective diameters of said first and second drive pulleys andto thereby vary the speed of said output member relative to the speed ofsaid input member, and control means for operating said drive means tovary the effective diameters of said drive pulleys, said drive meansincluding a first drive assembly operatively connected to said firstdrive pulley and a second drive assembly operatively connected to saidsecond drive pulley, said first and second drive assemblies eachincluding internally and externally threaded members which areoperatively connected to said control means and at least one of saidsections of an associated one of said drive pulleys, said control meansbeing operable in a first direction to provide relative rotation betweensaid threaded members to move said one of said sections of each of saiddrive pulleys relative the other section of each of said drive pulleysto increase the effective diameter of said first drive pulley and tosimultaneously therewith decrease the effective diameter of said seconddrive pulley, said control means being operable in a second direction toprovide relative rotation between said threaded members to move said oneof said sections of each of said drive pulleys relative to the othersection of each of said drive pulleys to decrease the effective diameterof said first drive pulley and to simultaneously therewith increase theeffective diameter of said second drive pulley, and compensator meansfor applying a biasing force tending to rotate one of the threadedmembers of each of said drive assemblies in such a direction relative tothe associated threaded member as to simultaneously iNcrease theeffective diameters of both of said drive pulleys to thereby take up anyslack which may result from an increase in the effective length of saiddrivebelt.
 16. A transmission assembly as set forth in claim 15 whereinsaid control means includes means responsive to a change in the speed ofthe output member upon an increase in the effective diameters of saidfirst and second drive pulleys for offsetting the change in speed of theoutput member by operating said drive means to vary the effectivediameters of said drive pulleys.
 17. A transmission assembly as setforth in claim 6 wherein said means responsive to the change in speed ofthe output member includes motor means for operating said drive means inresponse to a command signal indicative of a change in speed of theoutput member relative to a predetermined speed to thereby effectrelative movement between said sections of said drive pulleys, signalgenerator means for providing a feedback signal which varies as afunction of variations in the relative positions of said sections ofsaid drive pulleys, and means responsive to said feedback and commandsignals for interrupting operation of said motor means when saidfeedback signal is a predetermined function of said command signal. 18.A transmission assembly for varying the speed of an output memberrelative to the speed of an input member, said transmission assemblyincluding a first drive pulley operatively connected to said inputmember for rotation therewith and including a pair of sections mountedfor axial movement relative to each other to vary the effective diameterof said first drive pulley, a second drive pulley operatively connectedto said output member for rotation therewith and including a pair ofsections mounted for axial movement relative to each other to vary theeffective diameter of said second drive pulley, a main drivebeltextending around said first and second drive pulleys to therebyinterconnect said first and second drive pulleys, first drive meansoperable in a first direction to move said sections of said first drivepulley toward each other to increase the effective diameter of saidfirst drive pulley and operable in a second direction to move saidsections of said first drive pulley away from each other to decrease theeffective diameter of said first drive pulley, said first drive meansincluding a first externally threaded shaft, connector means forconnecting one of said sections of said first drive pulley to said firstshaft for axial movement therewith and for enabling said first shaft tobe rotated relative to said one section of said first drive pulley,first internally threaded nut means operatively connected to said firstshaft for effecting axial movement of said first shaft and said onesection of said first drive pulley relative to the other section of saidfirst drive pulley upon rotation of said first shaft to thereby vary theeffective diameter of said first drive pulley, second drive meansoperable in a first direction to move said sections of said second drivepulley toward each other to increase the effective diameter of saidsecond drive pulley and operable in a second direction to move saidsections of said second drive pulley away from each other to decreasethe effective diameter of said second drive pulley, said second drivemeans including a second externally threaded shaft, connector means forconnecting one of said sections of said second drive pulley to saidsecond shaft for axial movement therewith and for enabling said secondshaft to be rotated relative to said one section of said second drivepulley, second internally threaded nut means operatively connected tosaid second shaft for effecting axial movement of said second shaft andsaid one section of said second drive pulley relative to the othersection of said second drive pulley upon rotation of said second shaftto thereby vary the effective diameter of said second drive pulley, saidone section of said first drive pulley being locateD on one side of saidmain drivebelt and said one section of said second drive pulley beinglocated on the opposite side of said main drivebelt whereby relativemovement between said sections of said first and second drive pulleysupon operation of said first and second drive means tends to shift saidmain drivebelt axially with a minimum of deflection of said maindrivebelt, and control means for operating said first and second drivemeans to vary the effective diameters of said first and second drivepulleys, said control means including a first control pulley connectedto said first externally threaded shaft, a second control pulleyconnected to said second externally threaded shaft, a main controlpulley, control belt means extending around said control pulleys tothereby drivingly interconnect said control pulleys, said main controlpulley being rotatable in a first direction to effect operation of saidfirst drive means in its first direction by rotating said firstexternally threaded shaft in one direction relative to said firstinternally threaded nut means to increase the effective diameter of saidfirst drive pulley by moving said one section of said first drive pulleytoward said other section of said first drive pulley and tosimultaneously therewith effect operation of said second drive means inits second direction by rotating said second externally threaded shaftin said one direction relative to said second internally threaded nutmeans to decrease the effective diameter of said second drive pulley bymoving said one section of said second drive pulley away from said othersection of said second drive pulley, said main control pulley beingrotatable in a second direction opposite to said first direction toeffect operation of said first drive means in its second direction byrotating said first externally threaded shaft in another directionrelative to said first internally threaded nut means to decrease theeffective diameter of said first drive pulley by moving said one sectionof said first drive pulley away from said other section of said firstdrive pulley and to simultaneously therewith effect operation of saidsecond drive means in its first direction by rotating said secondexternally threaded shaft in said other direction relative to saidsecond internally threaded nut means to increase the effective diameterof said second drive pulley by moving said one section of said seconddrive pulley toward said other section of said second drive pulley, andcompensator means operatively connected to said first and secondinternally threaded nut means for applying biasing forces thereto toeffect relative rotation between said threaded nut means and said shaftsto move said shafts in a direction to increase the effective diametersof first and second drive pulleys in response to the occurrence of slackin said main drivebelt to thereby take up the slack.
 19. A transmissionassembly as set forth in claim 18 wherein said compensator meansincludes spring means operatively connected to said first and secondinternally threaded nut means for applying biasing forces thereto urgingsaid first and second externally threaded nut means into tightengagement with said first and second shafts.
 20. A transmissionassembly as set forth in claim 18 wherein said main control pulley has agenerally cylindrical drive surface means for drivingly engaging saidcontrol belt means, said drive surface means having an axial extentwhich is greater than the width of said control belt means to enablesaid control belt means to be shifted axially relative to said maincontrol pulley upon axial movement of said first and second controlpulleys.
 21. A transmission assembly as set forth in claim 18 whereinsaid control means further includes motor means for rotating said maincontrol pulley in response to a command signal to thereby effectrotation of said first and second control pulleys and operation of saidfirst and second drive means to vary the effective diameters of saidfIrst and second drive pulleys, signal generator means for providing afeedback signal which varies as a function of variations in the relativepositions of said sections of said first and second drive pulleys, andmeans for interrupting operation of said motor means when the feedbacksignal is a predetermined function of the command signal.